I've had questions on this too, and the general opinion seems to be that a) 12G allows for future upgrades to 20A circuits (if needed), and b) you put less stress on 12G wires due to the bigger capacity.

I use 12G wire everywhere, and I'm used to it now. Early on I cursed it a bit because 14G wire is much easier to twist and fold and fit it into boxes. With practice I got better at folding, and I like that you can push 12G wire through conduit and rarely have to fish or pull it.

I agree to use 12 gauge whereever you can. The demand on electrical circuits is only going to increase. Even as recently as 10 years ago, we didn't anticipate all the electrical gadgets that used to exist only in high-end, techno-freak homes, but now exist in almost all homes. The outlet once used for a TV and perhaps a VCR now regularly has the TV, VCR, DVD player, TIVO, and perhaps an entire home theater system. Families once got by with one computer, and that was often looked at as a luxury item. Now, it is commonplace for everyone to not only have their own computer, but also a laptop in addition to it. Virtually nobody had cellphones to charge at night. Now almost everyone does. Again, more electrical demands. The demands on electrical systems is only going to increase, so it is best to wire your circuits accordingly.